This invention relates to swash plate pumps and, in particular, to swash plate pumps used for steering pumps on marine craft.
Swash plate pumps are conventionally used in marine steering systems. Such a pump is physically mounted to the helm and has a drive shaft which is rotated by the helm. When the helm is rotated, the pump forces hydraulic fluid to the stern of the boat where the pressurized fluid moves a steering cylinder connected to the rudder, or propulsion unit in the case of outboard motor drives or inboard/outboard drives.
Several designs of swash plate pumps have been utilized in the past for different classes of marine craft. These pumps typically have a swash plate mounted on a member with a spigot extending outwardly therefrom. A rotor is rotatably mounted about the spigot and has a plurality of cylinder bores. Pistons are reciprocatingly mounted within the cylinder bores. The ends of the cylinder bores opposite the swash plate are conventionally configured to seal the cylinder bores against high-pressure hydraulic fluid.
A number of different designs have been developed to isolate adjacent cylinder bores from each other with respect to the high-pressure hydraulic fluid. For example, in some prior art designs the rotors are closed on the end of each rotor opposite the swash plate by blind drilling the cylinder bores. This does provide effective sealing. However the rotors are difficult to machine accurately and accordingly are relatively expensive. Another known design utilizes a rotor with open-ended cylinders, but the cover of the pump must be strong enough to withstand high pressure from the hydraulic oil pressurized by the pump. Accordingly the cover has to be of thick plastic or metal and held in place by strong fasteners. This makes the cover relatively expensive to construct and assemble.
It is an object of the invention to provide an improved swash plate pump which has a rotor with open-ended bores forming the cylinders, but without requiring the cover of the pump to take high pressure or high stresses.
It is another object of the invention to provide an improved swash plate pump which is economical to produce and assemble.
It is a further object of the invention to provide an improved swash plate pump which is rugged in construction and reliable in operation.
According to an embodiment of the invention, there is provided a rotary pump having a rotor with a first end, a second end opposite the first end, a central bore and a plurality of cylinder bores arranged about the central bore and extending completely through the rotor from the first end to the second end. There is a plurality of pistons, each piston being reciprocatingly received in one of the bores. A swash plate member has a swash plate adjacent to the second end of the rotor. A spigot extends through the swash plate member and the central bore of the rotor. The rotor is rotatably supported on the spigot. There is in an end cap connected to the first end of the rotor. The end cap closes off the bores at the first end of the rotor. A drive shaft is rigidly connected to the end cap and extends away from the rotor. There is a cover having an aperture rotatably receiving the drive shaft. The cover extends about the end cap and the rotor and is connected to the swash plate member.
Preferably, there is a bearing between the spigot and the rotor.
In one embodiment, the cover has a plurality of spaced-apart tabs and the swash plate member has a plurality of spaced-apart recesses. The tabs engage the recesses to connect the cover to the swash plate member.
Rotary pumps according to the invention offer significant advantages when compared with the prior art. They are easy to assemble and economical to produce, but provide reliable operation. This has been achieved in part by providing a rotor with cylinder bores which extend completely through the rotor. Such rotors are easier to machine and are more economical to produce than rotors having cylinder bores with one end closed by blind drilling. At the same time, the invention allows the use of relatively light weight and lightly stressed covers. This feature offers a more economical design and easier assembly compared with pumps having covers which must withstand relatively high hydraulic pressures. Furthermore, by using a special seal, the cover does not require a machined aperture to receive the drive shaft.